The kinetics of resensitization of Tetrahymena following recovery from effects of cycloheximide

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Abstract
Synchronized cells of Tetrahymena pyriformis strain GL‐C were exposed to cycloheximide (CHI) (0.2 μg per ml) from 40 to 140 minutes after the end of the heat synchronizing treatment. Recovery takes place during this treatment (Frankel, 1970). The CHI was washed out at 140 minutes. At various times after washout dividing cells were isolated in micro‐drops under oil, and one daughter was transferred to a test drop containing CHI (0.2 μ per ml). The generation time of both daughters was recorded, and the “percent prolongation” of generation time brought about by the test exposure of one cell to CHI was computed for each cell‐pair. This procedure was carried out for groups of cell‐pairs at different times after the end of the CHI pretreatment. Comparable tests were performed with two control series, one which had not previously been exposed to CHI and another for which CHI was present continuously. Comparison of the prolongation observed in control and experimental series demonstrated that cells which have earlier undergone recovery in CHI gradually become resensitized following washout of the drug. Cells progressively lose most of their original resistance in a period of somewhat over three cell generations; however, a small but significant fraction of this resistance is still retained seven to eight generations after the CHI pretreatment.